1. Field of the Invention
The present invention relates generally to electric heaters for fluids. More particularly, the present invention relates to apparatus and method for heating water in livestock watering tanks and in other containers.
2. Description of the Related Art
Electric heaters for livestocks watering tanks have been of several general types. One type has been the submerged heater that rests on the bottom of the watering tank. Another type has been the floating water heater. Other designs have been fastened or otherwise physically located with respect to the bottom of the tank.
Limitations of the prior art have included exposed heating elements that are subject to physical damage, inadequate thermal protection, and/or large geometric features. Such characteristics pose a threat of fire hazard, a threat of injury to livestock, a threat of unit damage, or tank size limitations.
Typical of the floating type are the units which are described by Landgraf in U.S. Pat. No. 2,561,932, issued Jul. 24, 1951; Brodie in U.S. Pat. No. 2,430,272, issued Nov. 4, 1947; Reitz in U.S. Pat. No. 2,454,091, issued Nov. 16, 1948; and Temple in U.S. Pat. No. 2,472,178, issued Jun. 7, 1949.
McKinstry, in U.S. Pat. No. 4,068,116, issued Jan. 10, 1978, greatly reduced the fire hazard by using a metallic strip to provide a heat flow path from the heating element to the thermostat. When submerged in water, because of water cooling the metallic strip, the metallic strip was relatively ineffective in transmitting heat from the heating element to the thermostat so that the thermostat was largely controlled by water temperature. However, upon occasions wherein an animal tossed the electric heater out of the water tank and into a pile of hay or straw, the metallic strip conducted the heat of the heating element to the thermostat rapidly, thereby avoiding overheating of the heating element and a fire hazard. Owen et al., in U.S. Pat. No. 4,835,366, issued May 30, 1989, improved on the electric heater of McKinstry by extending an end of the metallic strip of McKinstry, thereby providing additional cooling of the thermostat when the heating element is submerged in water.
Ward, in U.S. Pat. No. 4,599,973, issued Jul, 15, 1986, provided both floating and submerged electric heaters with the safety of McKinstry but with superior durability, reduced watt density, and more accurate sensing of the temperature of the heating element.
Accuracy, as it pertains to thermostatic control of electric heaters of the type discussed herein, does not mean that the thermostat turns off the electric heater at the temperature at which the temperature of the heating element equals the temperature setting of the thermostatic switch. Instead, accuracy refers to repeatability, the ability to accurately sense a temperature relationship, between the heating element and the thermostatic switch, under given conditions of immersion and/or non-immersion.
In spite of the advances made heretofore, none of the prior art has provided an electric heater which includes accuracy of sensing of the temperature of the heating element, durability of construction with the resultant freedom from accidental damage, and ultracompact design for use in small containers.